Zymogenetics' drug is a new version of interferon, called pegylated interferon lambda, that could have fewer side effects.

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It has also improved on Rebetron with a drug called Peg-Intron, a "pegylated" combination of interferon and polyethylene glycol (Peg for short).

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That might sound mundane, but the existing drugs used to treat hepatitis C, ribavirin and pegylated interferon, cause anemia and fatigue and must be taken for 48 weeks.

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Already, there is an expectation that Merck will be able to gain pricing and marketing advantages because it sells the current standard of care drugs, ribavirin and pegylated interferon.

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Roche, which already sells pegylated interferon (Pegasys) and ribavirin (Copegus), announced in May that in a small early-stage trial its polymerase inhibitor was effective in significantly reducing the viral load.

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The pharmaceutical company Roche, which produced the original version of pegylated interferon, said that it sought patents in order to guarantee the resources to re-invest in further 'cutting edge advances'.

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What the study shows is that if patients had undetectable levels of hepatitis C at one and three months, treating them with the current HCV standard treatment the combination of pegylated interferon and ribavirin for 48 weeks was no better than stopping at 24 weeks.

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